The long range goal of the proposed research is to understand how microtubule-associated proteins that are not motors participate in the function and organization of microtubules. These studies will focus on MAP 4, a microtubule-associated protein that is expressed during early development and in specific adult tissues in mice. Coding sequences for mouse and human MAP 4 have been obtained, a structural model for the protein defined, and novel transcripts observed in striated muscle and testis. A variety of approaches, including transfection and/or microinjection of protein fragments or fluorescently derivatized probes will be applied to deduce the regions of MAP 4 that are essential for function, and to ask whether or not there are domains that interact with cellular structures other than microtubules. Myogenic cell lines, in which induction of muscle-specific MAP 4 transcripts is observed, will be employed to examine the relationship between MAP 4 and tubulin isotype expression and distribution during myotube formation. Antisense technology will be used to ask whether MAP 4 is essential for normal cellular function, or events such as myogenesis or pre-implantation development. MAP 4 expression during mouse myogenesis, spermatogenesis and early development will be studied with correlative immunocytological and in situ hybridization analyses. Further molecular characterization of the coding sequences will be undertaken to determine the number, relationship, and mechanism of generation of the multiple MRNAS which presumably give rise to multiple protein isoforms. A minor project will be the completion of experiments that indicate the RII subunit of CAMP-dependent protein kinase mediates interaction of MAP 2 with the Golgi.